“…As we have already mentioned, the key point is that after firing a set A ⊆ V (G)\{q}, the value of b q goes down by exactly the size of A; this makes the function b q a powerful tool for running-time analysis in chip-firing processes. The seemingly different techniques of Tardos [46], Björner, Lovász and Shor [14], Chung and Ellis [19], van den Heuvel [28], and Holroyd, Levine, Mészáros, Peres, Propp and Wilson [29] all give bounds which are specializations of the running-time bound which we derive using b q ; see Remark 5.9.…”